Twin-field QKD in a real-world network

Quantum Key Distribution (QKD) is a technology that allows sharing secret cryptographic keys between two distant users (Alice and Bob), whose intrinsic security is guaranteed by fundamental principles of quantum mechanics. QKD is a mature technology even if one of the main remaining challenges is the integration of different solutions in already deployed telecommunication fiber networks, in particular in long-haul segments. An approach able to cover long distances is the Twin-field QKD (TF-QKD) protocol; TF-QKD exploits interference of optical pulses in a central untrusted node (Charlie), allowing to double the communication distance with respect to the conventional prepare-and-measure solutions. Here we present a solution to one of the main issues of Twin-Field QKD, the phase stabilization within the optical path, demonstrating a strong advantage in performances of real word TF- QKD and testing our solution in a segment of the Italian Quantum Backbone. Furthermore, we analyze in detail the expected gain in terms of key rate exploiting our stabilization technique in the main TF-QKD-based protocols, even when they are declared insensitive to the phase noise.